This invention relates to a unique blend of flame retardant components which provide a synergistic increase in ultraviolet (uv) stability of articles made from polymeric formulations containing the flame retardant components.
Typically, the uv stability of polymeric materials is provided by uv stabilizers which are colorless or nearly colorless organic substances. Ultraviolet radiation contains a quantum of energy sufficient to exceed the dissociation energy of covalent bonds found in polymeric materials. Without the use of uv stabilizers, visible light containing uv radiation tends to cause polymeric materials to discolor and become brittle; protective coatings to crack, chalk, and delaminate; and dyes and pigments to fade. Accordingly, additives which increase the light stability of flame-retarded formulations are generally required. For the purposes of this invention, the term "uv stability" shall also refer to the light stability of the formulation, blend, or articles made from such formulations or blends.
Classes of compounds used to reduce light-induced degradation of polymeric materials, include uv absorbers, hindered amines, nickel chelates, hindered phenols, and aryl esters. Commercially available uv absorbers include derivatives of 2-hydroxybenzophenones, 2-(2'-hydroxyphenyl)benzotriazoles, diphenylacrylates and oxalanilides. Hindered amine light stabilizers (HALS) include bis(2,2,6,6,-tetramethyl-4-piperidinyl) sebacate, CHIMASSORB.RTM. 944, and TINUVIN.RTM. 622. Depending on their structures, nickel chelates, such as CYASORB.RTM. UV 1084, IRGASTAB.RTM. 2002, and nickel dialkyldithiocarbamates, contribute to light stabilization of polymeric substances by decomposing hydroperoxides, scavenging free radicals, absorbing uv radiation, and quenching photoexcited chromophores. Suitable aryl esters include resorcinol monobenzoate, phenyl salicylate, substituted aryl salicylates, diaryl terephthalates, and isophthalates.
While the use of uv stabilizer additives provides a significant increase in the uv stability of polymeric materials containing them, there continues to be a need to increase the uv stability of macromolecular formulations without increasing the amount of uv stabilizer additive required.